Array declaration and initialization with structs

Question

I am trying to declare an array of structs, is it possible to initialize all array entries to a default struct value?

For example if my struct is something like

           typedef struct node
           {    int data;
                struct node* next;
           }node;

Is there a way to declare data to 4 and next to null? What about 0 and null?

If you mean "int data = 4;", the answer is NO. Not in C. http://stackoverflow.com/questions/13716913/default-value-for-struct-member-in-c — Vaibhav Desai, Oct 06 '13 at 20:10
Ok so if it isn't possible how would I check if next is empty? Just a simple NULL check or what? — Paul the Pirate, Oct 06 '13 at 20:13

score 3 · Accepted Answer · answered Oct 06 '13 at 20:08

3

Sure:

node x[4] = { {0, NULL}, {1, NULL}, {2, NULL}, {3, NULL} };

Even this should be fine:

node y[4] = { {0, y + 1}, {1, y + 2}, {2, y + 3}, {3, NULL} };

answered Oct 06 '13 at 20:08

Kerrek SB

1

But what if I have 100,000 entries in my array? Is there a more efficient way? – Paul the Pirate Oct 06 '13 at 20:10
For 100,000 entries you'd probably initialising from persistent storage so efficiency would not be a concern as the performance would be io-bound. Kerrek SB's answer stands as 'most likely the best solution' in my opinion so gets +1. – Bathsheba Oct 06 '13 at 20:13
@Bathsheba +1 I concur. There is no way via some magic declaration to initialize a sequence that increments ad-nausem to some declared upper-bound. Even a regular fixed trivial array, `int ar[N]` has the same restriction. The structure doesn't add extra complexity to that which is fundamentally impossible to begin with. – WhozCraig Oct 06 '13 at 20:17
So what happens if I have an array of nodes and I check to see if the array indices are null? – Paul the Pirate Oct 06 '13 at 20:19
@PaulthePirate: What are "array indices"?! – Kerrek SB Oct 06 '13 at 21:48
1

@PaulthePirate: Re 100000 entries: If you really want to *initialize* them, then you must spell out the initializer. If you're happy to assign the values after initialization, you can do it in a simple loop. (In C++ you could use templates to produce compact initializers, though.) – Kerrek SB Oct 06 '13 at 21:50
@KerrekSB Indices is the plural of index, so I just meant each node at a specific index. – Paul the Pirate Oct 06 '13 at 22:26

1 Answers1